1. Field of the Invention
The present invention relates to a porous silicon having a step and a method of preparing the same and, more particularly, to a vertical-alignment type porous silicon and a method of preparing the same which includes performing diffusion or ion implantation in respects to a silicon and forming pores having steps by using anodizing.
2. Description of the Related Art
A porous silicon has a peculiar structure and an excellent volume ratio and surface area. For this reason, preparation of the porous silicon and development of novel technology using the same come into the spotlight.
Furthermore, in recent years, light emitting devices, diodes, high performance sensors, thin film electrodes, integrated circuits, and fuel cells have been developed and studied by using the porous silicon in several spaces. In views of studies of characteristics of the porous silicon, the above-mentioned studies relate to a method of using physical properties of the porous silicon, a method of using a surface area, and a method of using electric properties.
For example, Korean Patent No. 0392152 discloses a method of preparing a porous semiconductor material which is subjected to liquid dipping and crystalline at a part or at an entire part thereof. The method further includes drying the porous semiconductor material by using a supercritical drying process.
In addition, Korean Unexamined Patent Application Publication No. 10-1998-032008 discloses a porous silicon, a surface of which is coated with a polymer to be very stable in the atmosphere, and a method of preparing the same.
The porous silicon may be prepared by electrochemically anodizing a single crystal silicon while the single crystal silicon is dipped in a hydrofluoric acid (HF) solution. Accordingly, the main factor in the preparation of the porous silicon is electric resistance and a current density of the silicon. However, in practice, various variables other than the electric resistance and the current density affect a pore size and structure of the porous silicon. With respect to this, the mechanism regarding affection of the variables on formation of pores is not known.
Therefore, the size of the pore which is formed during the preparation of the porous silicon is experimentally obtained for the most case. Accordingly, there are problems in that the porous silicon which is formed by using a known method has frequently an undesired pore shape and an alignment state is poor.
Additionally, there is a problem in that unnecessary processes such as epitaxial growth or a sealing process are added during the preparation and application of the porous silicon.
The unnecessary processes cause a waste of resources and energy, and enable unnecessary layers to be formed in addition to the desired porous layer.